1. Field of the Invention
This invention relates to a water pump for circulating engine cooling water in an automotive vehicle or the like.
2. Description of the Prior Art
Water pumps for circulating engine cooling water which have heretofore been widely used are generally of a structure in which an impeller is disposed on a portion of a rotary shaft rotatably supported in a housing fixed to an engine block through a bearing portion which extends into the engine block, and a pulley is disposed on the opposite side. The bearing portion is formed by an inner race, an outer race and rolling members interposed therebetween.
In recent years, due to the necessity of making the vehicle lightweight and making the vehicle compact for the saving of space, development of a compact, lightweight water pump has been desired, and an example, of such a pump is disclosed in Japanese Laid-open Utility Model Application No. 592/1984. The water pump described in said publication has achieved a reduction in number of parts and compactness by forming a rotary shaft 102 integrally with a pulley and forming a housing 104 and an outer race for a bearing integrally with each other, as shown in FIG. 4 of the accompanying drawings.
However, in the water pump described in the aforementioned publication, the housing 104 has a track surface for the rolling members 103 of the bearing and therefore must be made of steel for bearing against the rotating members. In this case, the housing 104 contacts the engine cooling water and the water entering the engine compartment and suffers from the problem of rusting. Therefore, it is necessary to subject the housing to a special surface treatment in order to prevent rusting. Further, since the housing 104 is formed of steel which has a specific gravity greater than aluminum heretofore used, no significant improvement can be obtained in terms of reducing the weight.
Also, the dimensions of the mounting portion of the housing 104 with respect to the engine body differ from vehicle to vehicle. Therefore, the housing 104 must be set in conformity with each vehicle individually even though the dimensions of the track portion of the bearing can be made common, and this is unsuitable for mass production.